In the sterilized packed rice, rice is main ingredient and may be mixed with additives such as glutinous rice or other grains and nuts. Moreover, in a pretreatment process for manufacturing the sterilized packed rice which can be preserved for a long time, there has been used a method of sterilizing the ingredient, in which it is feared that a microscopic organism will grow and multiply, by treating with an organic acid or dipping therein for a long time at a high temperature.
Generally, the sterilized packed rice is manufactured by filling food in a container, sealing it and then sterilizing it at high pressure and high temperature of about 130° C., thereby perfectly eliminating thermo-resistant bacteria as well as general bacteria.
However, in a packed food, since heat is slowly transferred from an edge portion thereof to a center portion thereof, the edge portion thereof is excessively heated when the center portion reaches the temperature of 130° C. and thus the taste of food is considerably deteriorated. On the contrary, in case that the packed food is sterilized at the high pressure and high temperature without the deterioration of food taste, the center portion thereof is not reached the desired temperature, and thus it is impossible to achieve the aseptic condition.
To solve the problem, there has been proposed, for example, a method of preparing packaged cooked rice and a method of sterilizing food in Korean Patent No. 265482 filed and granted to Shinwa kikai co., Ltd (FIG. 1).
In the method of preparing packaged cooked rice disclosed in Korean Patent No. 265482, rice which is washed and dipped in water so as to have a water content of 10˜30% is filled by a required amount in an opening tray and then transferred to a closed chamber so that the rice and container can be sterilized at the high pressure and high temperature/
The sterilizing process in the closed chamber is carried out in a short time of a few tens of seconds by using saturated steam with the high pressure of 2.7˜3.0 kgf/cm2 and high temperature of 100° C. or more, preferably 130˜140° C. Herein, the saturated steam with the high pressure and high temperature is intermittently flashed on the rice filled in the opening tray. In such intermittently and snatchily flashing process, for example, the flashing of the saturated steam with the high pressure and high temperature is repeatedly performed six to eight times in one cycle for 5 to 10 seconds.
In this case, an opening portion of the opening tray is coated with a plate member having honeycomb-shaped holes in the closed chamber in order to prevent the rice filled in each tray from being scattered by the intermittently flashing of the saturated steam.
After the sterilizing process in the closed chamber, water for cooking the rice is filled by a predetermined amount in each tray and the rice in the tray is put into a steam rice cooker and cooked by a typical method using the steam. Then the tray is transferred to a sealing unit by a transferring conveyor. In the process, the opening tray is passed through a tunnel booth in which a clean air generating device, such that bacteria is discharged by the clean air. When the tray is arrived at the sealing unit, inert gas is flashed on each tray, and a lid member is applied thereto and then sealed. The rice in the sealed tray is settled in its own steam for a desired period of time by a typical method and then cooled to the room temperature while the sealed tray is passed through a cooling-water bath. After the cooling process, the tray is dried and passed through a post-treatment process such as printing of pack date and expiration date, pinhole testing, weighing or the like, and packed with a desired case and then shipped.
The method of preparing the packaged cooked rice, disclosed in Korean Patent No. 265482 includes sterilizing, cooking and sealing processes. Particularly, in the closed chamber, the sterilizing process is performed repeatedly so that the saturated steam having the high pressure of 2.7˜3.0 kgf/cm2 and high temperature of 130˜140° C. is intermittently flashed six to eight times in one cycle for 5 to 10 seconds. In case of the shock manner that the saturated steam having the high pressure and high temperature is intermittently and snatchily flashed on the rice filled in the opening tray, it is apprehended that the rice is scattered. In order to prevent the scattering of the rice, the opening portion of the opening tray is coated with the plate member having honeycomb-shaped holes. Thus there is a problem that the structure thereof is complicated.
In the above-mentioned method, there is some doubt whether the thermo-resistant bacteria will be completely eliminated by the shock manner that the saturated steam having the high pressure and high temperature is intermittently and repeatedly flashed in a short time of a few tens of seconds, and also it is feared that external air may be introduced due to its own sealing manner that is partially opened. Moreover, there are some other problems that the separate clean room equipment, using of a food preservative and a heat sterilization process are needed additionally in order to maintain the sterilized condition and prevent bacterial penetration due to the introduction of the external air.
Further, in the above-mentioned method, since the finally prepared rice is provided in the semi-processed state, it is inconvenient that a user has to separately heat the packaged cooked rice to eat.